Fenitrothion degradation

Misra D, Bhuyan S, Adhya TK, et al. 1992. Accelerated degradation of methyl parathion, parathion, and fenitrothion by suspensions from methyl parathion- and />nitrophenol-treated soils. Soil Biol Biochem 24 1035-1042. 

The insecticide fenitrothion (0,0-dimethyl-0-4-nitro-3-methylphenyl thio-phosphate) can be measured in sea water and sediments by gas chromatography, using a flame photometric detector to determine P and S [387]. The degradation products of the organophosphorus insecticides can be concentrated from large water by collection on Amberlite XAD-4 resin for subsequent analysis [383]. 

In water, the percentage of these degradation products increased with time and amounted to one quarter of the remaining radiocarbon at 24 hr the quantity of 3-methyl-4-nitrophenol and both demethylated products is ca. 7% and 5.5%, respectively. Fenitrooxon was also detected. Because fenitrothion was stable in water under the present experimental conditions, these degradation products are presumably produced by fish metabolism. 

When rainbow trout were transferred to fresh water (24+24 and 24+48 in Table III), both fenitrothion and its radioactive metabolites were eliminated from the fish. Thus after 48 hr in fresh water, 60% of the radioactivity originally contained in the fish had been excreted into the water and the degradation products accounted for one half of the total radioactivity in water. Fenitrothion in the fish biomass steadily decreased, although the rate was lower than in running water as will be described belcw. 

Table V, VI and VII summarize the results of identification of the degradation products. The total radioactivity as well as intact fenitrothion decreased in snail and fish, and 3 consecutive applications of fenitrothion did not affect these concentrations very much. In contrast, in daphnids and in algae total radioactivity tendfed to increase with the lapse of time, mostly due to an increase of unextractable radioactivity and unidentified products, although the fenitrothion content was constantly decreasing...

They reveal that the ratio is not so high, at the maximum 180, and in fish it tends to decrease with longer incubation of the system, whereas in daphnids and algae the bioaccumulation ratio of fenitrothion was increasing under the present static conditions, due to quite rapid disappearance of fenitrothion in water. In any event, the bioaccumulation ratio was obviously far less than that of DDT and its degradation products. 

Table V. Distribution of C, fenitrothion and its degradation products in individual components of aquatic model ecosystem Water and soil.

The use of LC-APCI-MS makes it possible unequivocally to identify various degradation products from fenitrothion, ethyl-parathion and methyl-parathion, fenthion, and temephos (42,44). Moreover, LC-APCI-MS provides the best information on the transformation products. 

Durand, G. and D. Barcelo (1992). Environmental degradation of atrazine linuron and fenitrothion in soil samples. Toxicol. Environ. Chem., 36 225-234. 

Their volatilization from litter on the forest floor will also be appreciable. With the possible exception of carbaryl, their volatilization after being washed into the soil will be relatively low or insignificant because of their low volatility, low Henry s constants, Kh> and/or their high rates of degradation in the soil environment. The rapid disappearance of the phenoxy herbicides (2, 31) and the insecticide, fenitrothion (28) from vegetation and the forest floor is supporting evidence that volatilization is an important pathway for loss of applied pesticides from the forest canopy and litter on the forest floor. 

In order to evaluate the potential hazards chemical insecticides pose to forest environments, it is essential that adequate and reliable research data be generated on their environmental chemistry (distribution, persistence, movement, metabolic degradation, toxicity, fate, etc.). This paper gives a brief account of some laboratory and field research activities carried out at the Forest Pest Management Institute, Canadian Forestry Service to meet this requirement. Using two chemical insecticides which are extensively used now in forest insect control programs in Canada Viz aminocarb [Trade name, Matacil 4-dimethylamino-m-tolyl N-methylcarbamate] and fenitrothion [0,0-dimethyl 0-(3-methyl-4-nitrophenyl) phosphorothioate], studies conducted at the Institute to elucidate the environmental behavior and fate of forestry insecticides in general will be discussed. 

Laboratory Studies on Insecticide Degradation. Degradation in natural waters Stream water (pH 6.0) and sediment (organic content 36%) were taken from a small shallow stream (depth ca 20 cm, width oa 1.5 m) in the Goulais River watershed, a mixed conifer-deciduous forest area, ca 50 km northeast of Sault Ste. Marie, Ont., Canada. Two degradation studies in duplicate (one for aminocarb and another for fenitrothion) were set up according to Sundaram and Szeto ( 1 ). Aminocarb and fenitrothion (100 pg/L in acetone) were added separately to 1000 mL aliquots of sterilized (Ameco Sterilizer 1 h) and unsterilized stream water in either open or closed 1500 mL Erlenmeyer flasks. The latter were sealed with polyethylene snap caps which were removed once a day for about 1 min. to allow air exchange. The flasks were incubated at 15 0.2°C in an environmental chamber. Unfortified water... 

Figure 2. Degradation of fenitrothion in fortified natural and sterile stream water in open and closed flasks.

The rate constants (t l) and half-lives (t. ) for both autoclaved and non-autoclaved aminocarb and fenitrothion samples in open as well as closed flasks varied considerably (Figures 1 and 2). Rate constants were higher (more rapid degradation) in open flasks and half-lives were longer in closed flasks, showing that... 

Movement and degradation of fenitrothion in the water/sed-iment model The concentration of fenitrothion in non-autoclaved and autoclaved stream waters in the presence of sediment are shown in Figure 4. The concentration of fenitrothion decreased rapidly in water and increased rapidly in sediment, showing that fenitrothion has a greater tendency than aminocarb for translocation from water to sediment. Within 15 h, 94% (open flask) and 89% (closed flask) of the chemical in the non-autoclaved samples was lost from the aqueous phase and the corresponding concentrations in sediment were 43% and 66% respectively. The rapid translocation of this compound from water to sediment was probably due to its lipophilic nature (], ). Such a phenomenon was not very significant for aminocarb because it was present in water as a cationic species at pH 6.0. At the end of the experimental period (75 h), only 0.2% and 0.5% of the chemical remained in water whereas the sediments contained 19% and 31% of the fortified levels respectively. The rapid loss in the open flask is primarily attributable to volatilization coupled with some microbial degradation. In the absence of volatilization (closed flasks), the decrease in concentration in both the phases was lower. The presence of sediment therefore,... 

Figure U. Movement and degradation of fenitrothion in a water/sediment model.

The fate of fenitrothion in the environment has been a subject of great interest in Canada since the late 1960 s because of its use for control of the Spruce Budworm (Chorlstoneura fumiferana). Laboratory and field experiments have established that fenitrothion persists for only 1 to several days in natural waters and is degraded primarily by photolysis and microbial activity (1-4). Sorption by sediments, aquatic macrophytes and microphytes are also important paths of loss of the insecticide from the water column (2-5). 

The study was designed to examine the effect of sunlight intensity, the importance of volatilization and the extent of partitioning of fenitrothion and degradation products into sediment, plants and fish under field conditions. 

TLC separations were performed on silica-gel plates using two solvent systems 1. Toluene ethyl formate formic acid (5 7 1)(1 0) and 11. CCli, DCM methanol (5 7 1). Autoradiography was carried out by exposing TLC plates to X-ray film (Kodak NS-2T) for up to one month. Radioactive spots were scraped and extracted with methanol to establish the quantity of each degradation product. Rf s (fenitrothion = 1.0) of AF, MNP, F0 and SMF were 0.22, 0.76, 0.53 and 0.73 on System 1 and 0.83,... 

The cover over the shaded pond was removed at 17 days post-treatment in the first year of the study due to damage from a rain storm. Removal coincided with an unexplained increase in fenitrothion concentrations (Fig. 2). This increase was not observed in Year 2 when the shade was removed at the same time (Fig. 2). It is possible that disturbance of the water and sides of the ponds may have released sediment and plant-associated fenitrothion back into the water column, however, levels of degradation products did not increase proportionally. 

Figure 1. Disappearance of fenitrothion and degradation products in unshaded pond water following addition of the insecticide each year.

Table II. Half-lives (t 1/2) of fenitrothion and degradation products in pond water - Year 1 and 2.

The longer half-lives of fenitrothion and degradation products under shaded conditions indicates the importance of photolysis in the disappearance of the insecticide from shallow water bodies (1). However, the differences in half-lives were less than 2-fold compared to about 30-fold greater light intensity (in the visible range) under unshaded conditions (2 cm depth, Table I). 

The predominance of AF in sediments may account for its appearance in the water column at low levels during the first 21 days post-treatment AF is more polar than fenitrothion and would be expected to partition more readily back into the water column. AF has frequently been reported as a major degradation product of fenitrothion in stagnant pools (2)(5) and in flooded soils (10). 

Table V. Concentrations of fenitrothion or degradation products in duckweed extracts - Year 2.

Predicted and calculated flux of fenitrothion from water were similar although values were arrived at independently. Both results suggest that volatilization from water is slow compared to other paths of degradation of the insecticide which confirms predictions of the two-film theory of volatilization (17)(18). Losses of fenitrothion from surface films have been shown to be very rapid (2 ) but a surface film was not formed in the present work because the insecticide was mixed into the upper 10 cm of the water column. 

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